Due to the development of industry and increase in population, effective utilization of water resources has been required. Thus, reuse of waste water is very important. In order to achieve the effective utilization and reuse, it is necessary to purify the water, namely, to separate other substances from the water. As a method of separating other substances from liquid, various methods have been known, and there can be cited, for example, membrane separation, centrifugal separation, active carbon adsorption, ozonation, and aggregation, with which the removal of suspended solids or the like is conducted. Such methods make it possible to remove chemical substances such as iodine and nitrogen contained in water, which greatly affect on the environment, and to remove oil, clay and so on dispersed in water.
Meanwhile, in recent years, technologies of recovery and removal of iodine have been drawing an attention. A usage range of iodine is wide, and iodine is used in a wide range of fields such as a chemical field in which iodine is used in a chemical fiber and a thermal stabilizer, in addition to a medicinal field in which iodine is used in a disinfectant and the like. Iodine has many isotopes, in which iodine131 (131I) is a radioisotope, which is generated as a daughter nucleus when uranium235 (235U) undergoes fission.
Therefore, there is a case where the radioiodine is contained also in a radioactive material discharged in a large amount when a problem occurs in a nuclear power plant, and such radioiodine may be mixed in the air or in waste water. Therefore, the removal of radioiodine when the radioiodine is mixed in the air or in the waste water, has become a task.
As a method of removing iodine, there is a method of removing iodine by using an adsorbent in which, for example, silver is supported on zeolite, and calcium ions are eccentrically located on a peripheral portion of the resultant. In this case, it is possible to apply an apatite coating to a surface of the adsorbent, so that it is possible to suppress an elution of silver supported on zeolite from the adsorbent under a high temperature condition.
However, zeolite and silver are not firmly chemically bonded, so that there is a disadvantage that silver is eluted when a treated solution takes an acidic pH value, for example. Further, since zeolite is a powder with several μm and has a crystallinity, it is difficult to generate zeolite with a large particle size, and thus a size of the adsorbent to be obtained corresponds to a particle size of several μm, so that a handling is difficult, which is also a disadvantage. In order to solve the latter problem, it can be considered to perform granulation using a binder or the like, but, a new problem has arisen such that the number of manufacturing processes of the adsorbent increases, resulting in that a manufacturing cost of the adsorbent increases.